This invention pertains to disc-handling systems and methods of a type, for example, particularly useful for transporting semiconductor wafers having a highly sensitive surface which can be very easily damaged or contaminated.
Heretofore, disc-handling systems have suffered from an inherent inability to both put a disc down onto an expansive surface at least co-extensive with the disc and to pick up such a disc without entering beneath or engaging the disc. This limitation has prevented the ready transfer of discs onto and off of surfaces, such as moving belts, rotating tables, stationary pedestals, and other broad surfaces extending beyond the edge of the disc.
Thus, placement of a disc on a chuck has usually required that the disc extend beyond the edge of the chuck so that a portion of the disc can be engaged from beneath in order to lift it. The disc must then be larger than the chuck on which it may be placed for testing, treatment, examination or the like.
In the past, discs such as semiconductor wafers have been transported by means of an air track as may be described with respect to the prior art FIGS. 4 and 5. As shown in FIG. 4, a portion 11 of an air track of the prior art is represented diagrammatically as having a generally flat surface 12 for supporting a generally circular disc 13, such as a semi-conductor wafer. A manifold 14 in the form of a drilled opening extends along the centerline of portion 11 for receiving air under pressure to be discharged via the uniformly spaced outlets 16 at an angle having a vectorial component extending in the direction in which it is desired to transport disc 13. The side edges 17 serve to guide disc 13 along a predetermined path.
In the foregoing type of construction, the top surface of disc 13 is necessarily the sensitized, delicate and easily contaminated precious portion of the disc in view of the fact that, if the air supply is terminated, the disc drops and would therefore scrape along surface 12 damaging any semiconductor configurations or material applied to the undersurface of the disc. FIG. 5 shows a diagram of the upward flow of air 18 which passes around the side edges of disc 13 and swirls downwardly onto the central portion of the top surface of the disc. Any contaminants which may have been entrained in the air stream 18 are therefore deposited on the top surface of the disc.
From inspection of FIG. 4, it is readily evident that, once the air pressure is appropriately adjusted so as to transport a given weight of disc 13, the air pressure will be too great if a much lighter weight disc 13 is dispatched onto the surface 12. In this case the lighter weight disc 13 can be blown from the track, thereby (not infrequently) destroying substantially the entire disc.
An important advantage of the disc-handling system of the present invention is found in its ability to precisely place, retrieve and transport discs relative to a work surface which is larger than the disc itself without engaging or entering beneath the disc so as to permit use of the system with both moving and stationary disc-receiving surfaces. Moreover, the above-described and other problems are believed to have been overcome by the disc-handling system of the present invention.